Since the early 1970's, when concern over the environment caused many areas of the United States to restrict or eliminate the use of phosphates in heavy duty laundry detergents, the industry has been turning to other sources for the control of water hardness ions in wash water, i.e. calcium and magnesium. More recently, the desire to replace phosphate detergent builders with environmentally safe substitutes has become apparent in other parts of the world.
With the advent of liquid heavy duty detergents, sodium citrate, the trisodium salt of citric acid, has become the builder of choice. Sodium citrate is suitable for use as a builder in heavy duty laundry detergents because of its ability to sequester positively charged calcium and magnesium ions found in tap water and, unlike phosphate builders, it is environmentally safe. It is especially suitable for inclusion in liquid detergent formulations because, unlike other environmentally safe detergent builders, trisodium citrate is soluble therein.
Sodium citrate containing, liquid detergent formulations have enjoyed considerable success in the United States where normal washing temperatures range from about 20.degree. to 50.degree. C. Such formulations have not been successfully introduced in regions such as Western Europe, where normal washing temperatures typically range from 60.degree. to 90.degree. C., because of the widely held belief that sodium citrate is not an effective detergent builder at these elevated temperatures. This is reported in Synthetic Detergent, 7th Edition, p. 93, A. S. Davidsohn & B. Milwidsky; John Wiley, New York (1987) and "Builders in Liquid Laundry Detergents", Colin A. Houston, Proceedings from the Second World Conference on Detergents, American Oil Chemists Society, 1987.